The present invention relates generally to communication system and method, and more specifically, to a system and method for providing communications where the media limit electromagnetic energy transfers.
Traditionally, in environments such as underground mines, industrial structures, and commercial complexes where electromagnetic energy transfer is blocked or limited by the media or obstacles, communication has been achieved by hardwired systems such as telephone lines. The demand for higher workers"" safety and for higher productivity stimulated product developments in an effort to use wireless two-way radios. Conventional wireless communication over long distances in these environments is not possible because the mine overburden (earth, water rock, etc.) and steel reinforced concrete in structures attenuate and dissipate the electromagnetic energy before it reaches its destination. Much of the development effort was directed to solve needs specific to the mining industry.
To meet mining communication requirements, it is necessary to have two-way communication between underground workers inside the mine and persons on the surfaces, and two-way communication between workers inside the mine and other workers inside the mine. In the mid 1970""s the US Department of the Interior Bureau of Mines (USBM) engaged in efforts to develop wireless communication means for trapped miners. Collins Radio (USBM Contract No. HO133045) and General Instrument (USBM Contract No. JO35017) developed hand-held wireless transmitters that transmitted a tone (i.e., single frequency) that could be used by trapped miners to help surface rescue personnel to locate the trapped miners. Wide band (needed for voice or data) communication was considered impossible because of the amount of energy that would have to be in the transmitting antenna inside the mine that could cause a gas explosion in case of damage to the antenna.
USBM Report #RI9377 discusses and demonstrates the implementation of a method by which a wireless transmitter on the surface using a loop antenna could send a warning signal from the surface into the mine in case of an emergency, but no message could be sent from inside the mine to the surface. The transmitter antenna was fed from a 1 kW amplifier. The receiving antennas inside the mine were made of short high-permeability wound ferrite cores. Transmission from inside the mine to the surface was impossible.
Mine Site Technologies (www.minesite.com.au), and TeleMagnetic Signal Systems (NIOSH Report RI 9641-ISSN 1066-5552), developed one-way communication products to send warning signals to miners based on this USBM report. These systems are only capable of transmitting warning signals into the mine. Voice transmission is impossible in these systems. The signals transmitted from the surface to the interior of the mine cause the miner""s cap lamp to flash. In the case of Mine Site Technologies, a warning message is displayed on an LCD. In the case of TeleMagnetic Signal Systems, the flashing lamp is a warning to evacuate the mine. If in addition a red LED is turned on, the miner must go to a telephone to receive the message.
U.S. Pat. No. 4,652,857 discloses a method and apparatus for a non-real time, two-way, wide-band communication for power restricted environments. The invention makes it possible to communicate voice or data from the surface of a mine into the mine, and from inside the mine to the surface. The method requires a loop antenna on the surface and a loop antenna inside the mine. The functioning of the system depends on magnetic Faraday coupling between the two antennas. To keep the antenna current inside the mine small enough to prevent an accidental explosion, the system trades power for bandwidth. This results in non-real time communication from inside the mine to the surface. For example, a six seconds message from inside the mine may take 60 seconds to reconstruct on the surface. Such operation is acceptable for emergency communication, but not for daily operational communication.
Several approaches have been advanced for communications inside a mine. A paper by Dobroski and Stolarczyk in IEEE Trans. on Industry Applications Vol. IA-21 July/August 21, 1985 describes a method for transmission inside a mine using medium frequency. U.S. Pat. Nos. 4,879,755, 5,093,939, and 4,777,652 further teach the application of this concept. The methods taught by these patents depend on residual conductors that happen to be in the mine naturally or from previous structures. Signals xe2x80x9chopxe2x80x9d from one conductor to another. Operation in arbitrary mines, therefore, cannot be guaranteed. The medium frequencies require the use of two-way radios that are larger than conventional two-way radios, and antennas that are so large that they must be carried by the miners either as shoulder straps which loop over a person""s shoulder or they are sewn into a jacket that must be worn by the miner. Conspec/RIMtech, Raton Technologies, and others built products based on this method.
The most widely used method for wireless communications inside a mine uses so called Leaky feeders or radiating transmission lines. U.S. Pat. Nos. 5,432,838, 5,669,065, 5,697,067, and 5,809,429 discuss application of this method. Such a system makes use of transmission lines (also referred to as feeders or radiax antennas) that consist of coaxial cables with incomplete shielding so that electromagnetic energy is radiated from the cable along the length of the cable that can be received by mobile radios, and the antenna can receive signals transmitted from the mobile radios. The system also has a base station and amplifiers at spaced distances along the transmission lines. The lines are heavy, on the order of ⅝ inch in diameter. They are expensive and expensive to install and maintain. Since energy is gradually disseminated along the line and the total energy is restricted by FCC and safety regulations the energy at any distance from the line is relatively small. The radios between which communication is to be established must be in close proximity to the lines, requiring an extensive cable network throughout the mine. El-equip Inc., Tunnel Radio, Mine Radio Systems and others built products based on this method.
Therefore, it is highly desirable to have a system for providing a two-way bi-directional voice communications as well as digital communications in the environment where electromagnetic energy transfer is blocked or limited.
The present invention is directed to a method and system for communication, preferably wireless, within an energy-transmission-limited environment such as an underground large industrial facility or mine. In these environments, person-to-person wireless communications are not feasible using traditional communications devices. The present invention enables communications in such an environment using off-the-shelf hand-held radios tuned, for example, within the UHF frequency band. The frequency band is not, however, limited to UHF frequency band. In addition, digital information and control signals such as those acquired by automated sensors can be routed through the facility.
Site-wide communications are enabled by strategically locating RF transceivers throughout the site such that areas within the site in which communications are desired are within range of at least one of the RF transceivers. In the present invention, a plurality of RF transceivers, each one tuned to a frequency, is placed at each location to enable multiple independent channels of communication. The present invention provides, for example, four or more different channels of communication.
At each location, the RF transceivers are connected to a control unit. A control unit, which may be designated as either a master or interface unit, provides power to the transceivers and allows for bi-directional communication of audio or voice, control and status information between the control unit and each transceiver. In this way, the control unit can force the RF transceiver to transmit an audio signal so that anyone within range of the transceiver hears the audio message on their portable hand-held radio. Similarly, when anyone within range of RF transceiver wishes to communicate with another individual, they are enabled to talk into their portable hand-held radio, while pushing the xe2x80x9ctalkxe2x80x9d or xe2x80x9ctransmitxe2x80x9d button, for example. The nearest RF transceiver receives the broadcast and informs the control unit to which the nearest RF transceiver is connected that the transceiver is receiving a valid RF broadcast. The RF transceiver also sends demodulated voice signal to the control unit. In cases where the transmission/reception ranges of the RF transceivers overlap, such that several control units may receive the same RF signal through their corresponding RF transceivers, the control units have the ability to determine the strength of the received signal at the RF transceiver. In this way, only the control unit that is receiving the strongest signal may send the received signal to all other control units in the network. The signal may be digitized.
The control units may be networked to each other using standard network-type Categoy-5 or equivalent cables. In this way, an audio signal, e.g., speech, received by a RF transceiver connected to a control unit is converted from analog signal to digital representation of the signal and sent over the network connections to the other control units connected in the network. When the other control units receive the digitized speech waveform over the network, the control units convert the signal back to analog speech waveform and force the RF transceiver to transmit the signal so that anyone located within range of the transceiver will be able to hear the message on their own hand-held radio. The present invention provides multiple independent channels of communication. These channels of communication may be used to transmit additional information along with the digitized speech signal. The additional information may include digitized speech transmission channel as well as other control information that may be transmitted with the digitized speech waveform.
The control units of the present invention may also include one or more electronic devices such as portable computers, sensors, or automated equipment connected to the control units. The connection may be accomplished by, e.g., using standard RS-232 data communications protocol.
In the present invention, information transferred in the network may be monitored or controlled remotely from within the site. The present invention provides, for example, one RS-232 connection to each control unit.
In one embodiment, each control unit is either designated as a master or an interface unit. In one embodiment, a site includes one control unit designated as the master unit with one or more interface units. The master and interface units may comprise identical electrical hardware. In addition, the master and interface units may include software that controls the units. For example, master unit includes software to control the timing and flow of data over the networked connection.
Additionally, for troubleshooting problems that may occur during installation and maintenance of the system, the control units include several status indicators (LEDs). The status indicators of the present invention may be used to quickly identify network-related errors that may occur over the connection between control units. For example, the status indicators may be used to determine such problems as the existence and location of broken network connections and noise-induced communications errors.
The present invention also includes through-the earth (xe2x80x9cTTExe2x80x9d) communication system to enable two-way voice as well as digital communication between the surface of the mine and the mine interior. In one embodiment, the TTE system of the present invention need not have a hard-wired connection between the transceiver on the mine surface and the transceiver in the mine interior. The communication in this embodiment may be accomplished by magnetic coupling of energies between the antennas, for e.g., by low frequency n the range of 3,000 Hz and 8,000 Hz between loop antennas connected to TTE transceivers. The transceivers of the present invention in one embodiment utilize single sideband modulators to modulate voice and/or digital signals. The signals are demodulated and filtered at a receiving end of a transceiver. A comb filter attenuates noisy signals with drifting harmonics.
The present invention also includes powerline communication module to provide power to the transceivers and also to enable bi-directional communication of audio/voice, control and status information between the module and one or more transceivers. The powerline communication modules include an alternating current (xe2x80x9cACxe2x80x9d) power modem capable of connecting to existing AC powerlines. The powerline communication modules may communicate via the AC power modem through existing AC powerlines to other powerline communication modules.
The present invention also includes a novel method of connections between multiple power systems or phases. Traditional system of using a capacitor bridge only to connect multiple power systems does not work reliably when more than two power systems are being connected. Using more than one capacitor bridge in a system, for example, to connect more than two power systems to the same powerline communications network does not work with the traditional systems. To overcome the shortcomings of the traditional systems, the novel bridging method leaves two power systems or phases that are being bridged as independent and galvanically-isolated with only a galvanically-isolated RS-232 serial connection between the two power systems or phases. In this way, network data, e.g., digitized voice and digital process data, may be passed between two powerline communications modules, one on each power system or phase, thereby effectively bypassing the AC powerline medium and instead using a dedicated, galvanically-isolated high-speed serial connection so that the two power systems or phases are left isolated.
Further features and advantages of the present invention as well as the structure and operation of various embodiments of the present invention are described in detail below with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements.